New codon codes for a different amino acid →change in primary structure of protein
Degenerate nature of genetic code : new codon may still code for the same amino acid leading
to no change in protein synthesised
, 2
Position & involvement of amino acid in R group interactions within protein determines
impact of new amino acid on function of protein
Eg. amino acids have role in active site = enzyme can’t act as a biological catalyst
● Deletion
● Insertion
Frameshift mutation
Triplet code (sequence of bases transcribed consecutively in non-overlapping groups of 3 =
reading frame of a sequence of bases)
Addition & deletion of nucleotide shifts reading frame = change every successive codon from
the point of mutation
N. nucleotides changed is multiple of 3 = reading frame not changed, but protein affected as
new amino acid added
Effects
No effect: normally functioning proteins still synthesised. In non-coding regions (introns) or
code for same amino acid
Damaging: phenotype affected negatively as protein not synthesised or non-functional
Beneficial: synthesised protein results in new useful characteristic in phenotype
Causes
Rate of mutation increased by mutagens (bio, physical or chemical agent)
Spontaneous depurination / depyrimidination → insertion of incorrect base through complementary
base pairing in DNA replication
Free radicals (oxidising agents) affect structures of nucleotides & disrupt base pairing
Antioxidants (anticarcinogens) negate effects of free radicals
★ Ionising radiation (eg. X-rays) break 1+ DNA strand
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